Hey, I also have problem like you. But when I was in form 3, I realize I need to learn English before I regret when seeing my PMR result. So, ways I do to improve my grammar are, I read English story books. Just read children story book before you go to the novel. And you also can read on wattpad. There have a lot of stories in English and also in Malay. The best is, you can read it free.
Next, always use English when talking with your friends and ask them to help you how to pronounce the hard vocabulary. My friends always help me when I need to.
Use dictionary to find the words you did not understand.